Octane ?

willbrooks2 · Feb 22, 2006

What octane should i use in my 95 mustang gt? The only mods are cold air and 14* timing advance.

Swarzkopf · Feb 22, 2006

Probably 92 or better with that advanced timing.

drakesdad · Feb 22, 2006

I agree

JJ95GTID · Feb 22, 2006

Go as low as you can without pinging. Really depends on the condition and tune of your car. You could have lots of carbon build-up in the combustion chambers which will increase compression and can increase chance of pinging. Some people have to run 92 octane and 8* of timing. Some others run 12* and 87 octane. You just have try and see what will work.

Black95GTS · Feb 22, 2006

willbrooks2 said:
What octane should i use in my 95 mustang gt? The only mods are cold air and 14* timing advance.

However low you can get away with without pinging. You're probably around the 91 level right now at 14* on stock iron heads.

It definately depends on the car though. I can run mine at 13 degrees advance on 89 octane and not ping at all. Some guys have to turn timing back to 8 or 9 degrees just to run 87!

Adam

HISSIN50 · Feb 22, 2006

Adam, you got that little box that gets your puter running like it should have originally - that's cheating! (J/K man - I am just jealous).

All the replies are right on. Just gotta see what happens for your car on whatever blend of fuel you have right now, in your ambient temps.

Good luck.

94gts · Feb 22, 2006

i use premium in both of my cars, even my POS 90 accord with 275k on the odometer. 87 is cheap **** and smells like crap

It pisses me off when people in their bmws, benzes, caddys, etc come to my gas station and say "Fill it up with regular," even when it says PREMIUM FUEL ONLY inside the gas door. If only people knew there was actually a reason for that. I often want to smack these retards.

legalize420 · Feb 22, 2006

i get better gas milage on 87 so thats what i use. my timing is at 14*

94gts · Feb 22, 2006

legalize420 said:
i get better gas milage on 87 so thats what i use. my timing is at 14*

I didnt buy a mustang for gas mileage.....

Rootus · Feb 22, 2006

94gts said:
I didnt buy a mustang for gas mileage.....

Gas mileage is just a nice bonus. All else being equal, you get more horsepower with less octane, so that is why you go as low as you can without hearing detonation.

94gts · Feb 22, 2006

i remember a chem experiments i did a couple years ago in school, something about lower octane burning faster....therefore, the higher octane fuel burns slower, thus you get better mileage with 93 than 87.

Rootus said:
that is why you go as low as you can without hearing detonation.

Why would you want to be at the "point" of detonation? It doesnt make much sense to me that you would want your car to be just above the point of anything just to gain a farts worth of horsepower. Thats like running your motor 2 quarts low on oil so there is less resistance on the crankshaft.

Rootus said:
you get more horsepower with less octane

I dont see why anyone would use 87 in a h/c/i car.

If high octane is so bad, why is there race gas?

HISSIN50 · Feb 23, 2006

Couple things crossed my mind. If you look at dyno sheets, there is a point where power falls off with an increase in timing advance, but it generally happens before pinging occurs. Therefore running on the ragged edge of detonation could be yielding a decrease in power, as well as taking a chance on seeing detonation.

Octane ratings are a measure of the resistance to knock. One needs to optimize the timing setting and octane rating relationship. The higher octane's resistance to knock is what allows more timing to be run. The explosion is often in the same relative piston displacement however, whether using low or high grade, so long as timing is optimized for the given grade.

If we had piezo sensors, then the dynamic would be different. But we dont, so that is my take.

legalize420 · Feb 23, 2006

94gts said:
I didnt buy a mustang for gas mileage.....

well good for you. neither did i.

Black95GTS · Feb 23, 2006

94gts said:
If high octane is so bad, why is there race gas?

Race gas is used on primarily on power adder cars putting down a lot of power. The higher the octain, the more spark advance can be run without detonation, thus more horsepower, to a point.

This is also the reason for the new Methanol injection kits... the whole purpose of the kit is to decrease the chances of detonation in a boosted application and allow more advance.

Example, you are running a nitrous car. The instructions tell you to back down the timing 2 degrees per 50 shot and run 91 octain. But instead, you run race gas at some 100 octain (for example). Now, instead of backing down timing and losing a little bit of power to avoid knock, you can maintain or in some cases actually advance your timing and still avoid knock while running the same size shot.

I'm basically repeating Mr. Wizard's post. But I want to make sure we are all on the same page.

Adam

94gts · Feb 23, 2006

Black95GTS said:
Race gas is used on primarily on power adder cars putting down a lot of power. The higher the octain, the more spark advance can be run without detonation, thus more horsepower, to a point.

I know the purpose of race gas. I was just being sarcastic since i i was getting the feeling that people were saying lower octane makes more horsepower

Scott_95GT · Feb 23, 2006

There are many factors that can go into how much timing you can get away with. Octane, outside temp, health of your motor, tune, ect.

Out here in California, the best gas you can get is 91 octane (which sucks balls). Combine that with summer temps over 100* and forget it. I was running 12* for awhile, but I just went back to 10* to be safe.

WHITE94COBRA · Feb 23, 2006

I have a shell station off of alicia parkway that sells "pump" 110 octane. $4.25 a gallon, and i'm in so cal. I have never actually bought it though.

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